Hydroxide promotes ion pairing in the NaNO2-NaOH-H2O system

Nitrite (NO2-) is a prevalent nitrogen oxyanion in environmental and industrial processes, but its behavior in solution, including ion pair formation, is complex. This solution phase complexity impacts industries such as nuclear waste treatment, where NO2- significantly affects the solubility of other constituents present in sodium hydroxide (NaOH)-rich nuclear waste. This work provides molecular scale information into sodium nitrite (NaNO2) and NaOH ion-pairing processes to provide a physical basis for later development of thermodynamic models. Solubility isotherms of NaNO2 in aqueous mixtures with NaOH and total alkalinity were also measured. Spectroscopic characterization of these solutions utilized high-field nuclear magnetic resonance spectroscopy (NMR) and Raman spectroscopy, with additional solution structure detailed by X-ray total scattering pairwise distribution function analysis (X-ray PDF). Despite the NO2- deformation Raman band's insensitivity to added NaOH in saturated NaNO2 solutions, 23Na and 15N NMR studies indicated the Na+ and NO2- chemical environments change likely due to ion pairing. The ion pairing correlates with a decrease in diffusion coefficient of solution species as measured by pulsed field gradient 23Na and 1H NMR. Two-dimensional correlation analyses of the 2800-4000 cm-1 Raman region and X-ray PDF indicated that saturated NaNO2 and NaOH mixtures disrupt the hydrogen network of water into a new structure where the length of the OO correlations is contracted relative to the typical H2O structure. Beyond describing the solubility of NaNO2 in a multicomponent electrolyte mixture, these results also indicate that nitrite exhibits greater ion pairing in mixtures of concentrated NaNO2 and NaOH than in comparable solutions with only NaNO2.

Ion-ion interactions enhance aluminum solubility in alkaline suspensions of nano-gibbsite (α-Al(OH)3) with sodium nitrite/nitrate

Despite widespread industrial importance, predicting metal solubilities in highly concentrated, multicomponent aqueous solutions is difficult due to poorly understood ion-ion and ion-solvent interactions. Aluminum hydroxide solid phase solubility in concentrated sodium hydroxide (NaOH) solutions is one such case, with major implications for ore refining, as well as processing of radioactive waste stored at U.S. Department of Energy legacy sites, such as the Hanford Site, Washington State. The solubility of gibbsite (α-Al(OH)₃) is often not well predicted because other ions affect the activity of hydroxide (OH^-) and aluminate (Al(OH)₄^-) anions. In the present study, we systematically examined the influence of key anions, nitrite (NO₂^-) and nitrate (NO₃^-), as sodium salts on the solubility of α-Al(OH)₃ in NaOH solutions taking care to establish equilibrium from both under- and oversaturation. Rapid equilibration was enabled by use of a highly pure and crystalline synthetic nano-gibbsite of well-defined particle size and shape. Measured dissolved aluminum concentrations were compared with those predicted by an α-Al(OH)₃ solubility model derived for simple Al(OH)₄^-/OH^- systems. Specific anion effects were expressed as an enhancement factor (Al_enhc) conveying the excess of dissolved aluminum. At 45 °C, NaNO₂ and NaNO₃-containing systems exhibited Al_enhc values of 2.70 and 1.88, respectively, indicating significant enhancement. The solutions were examined by Raman and high-field ²⁷Al NMR spectroscopy, indicating specific interactions including Al(OH)₄^--Na⁺ contact ion pairing and Al(OH)₄^--NO₂^-/NO₃^- ion-ion interactions. Dynamic evolution of the α-Al(OH)₃ particles including growth and agglomeration was observed revealing the importance of dissolution/reprecipitation in establishing equilibrium. These studies indicate that incomplete ion hydration, as a result of the low water activity in these concentrated electrolytes, results in: (i) enhanced reactivity of the hydroxide ion with respect to α-Al(OH)₃; (ii) increased concentrations of Al(OH)₄^- in solution; and (iii) stronger ion-ion interactions that act to stabilize the supersaturated solutions. This information on the mechanisms by which α-Al(OH)₃ becomes supersaturated is essential for more energy-efficient aluminum processing technologies, including the treatment of millions of gallons of Al(OH)₄^--rich high-level radioactive waste.

[Oxidized fibrinogen and its relationship with hemostasis disturbances and endothelial dysfunction during coronary heart disease and myocardial infarction]

The highest oxidative modification of fibrinogen was found in acute myocardial infarction (MI) men and it was 1.26 and 1.56 times higher in comparison with coronary heart disease (CHD) men with anamnesis of MI and with men without CHD, respectively. Increased oxidized fibrinogen level correlated with increased levels of plasma lipid peroxidation products, Willebrand factor, fibrin degradation products, accelerated leukocyte-platelet aggregation and decreased level of plasma NO metabolites. Associations of oxidized fibrinogen with MI and typical parameters of thrombosis and hypercoagulatory hemostasis disturbances and endothelial function were revealed.

[Prevalence of electrocardiographic signs of pulmonary hypertension in a sample of male population of Novosibirsk]

Prevalence of ECG signs of right ventricular hypertrophy and pulmonary hypertension was assessed in a representative sample (n=715) of nonorganized male population (age 25-64 years) of Novosibirsk studied within a framework of WHO MONICA project. Other methods of investigation included Rose questionnaire, anthropometry, ECG interpreted with Minnesota code, and echocardiography. Echocardiography data were used as reference for determination of sensitivity and specificity of ECG-criteria of pulmonary hypertension.

Production of stress retraction by left- and right-hemisphere-damaged patients

An acoustic-perceptual investigation of a phonological phenomenon in which stress is retracted in double-stressed words (e.g., thirTEEN vs THIRteen MEN) was undertaken to identify the locus of functional impairments in speech prosody. Subjects included left-hemisphere-damaged (LHD) and right-hemisphere-damaged (RHD) patients and nonneurological controls. They were instructed to read sentences containing double-stressed target words in the presence of a clause boundary or its absence. Whereas all three groups of subjects were capable of manipulating the acoustic parameters that signal a shift in stress, there were some differences between the performance of the patient groups and that of the normal controls. Further, stress production deficits were more severe in LHD aphasic patients than in RHD patients. LHD speakers exhibited deficits in the control of both temporal and F0 cues. Their F0 disturbance appears to be secondary to a primary deficit in temporal control at the phase or sentence level, as an increased number of continuation rises found for the LHD patients seemed to arise from lengthy pauses within sentences. Findings are highlighted to address the nature of breakdown in speech prosody and the competing views of prosodic lateralization.

The effect of compressed speech on the ability of right-hemisphere-damaged patients to use context

The ability of RHD patients to use context under conditions of increased processing demands was examined. Subjects monitored for words in auditorily presented sentences of three context types-normal, semantically anomalous, and random, at three rates of speech normal, 70% compressed (Experiment 1) and 60% compressed (Experiment 2). Effects of semantics and syntax were found for the RHD and normal groups under the normal rate of speech condition. Using compressed rates of speech, the effect of syntax disappeared, but the effect of semantics remained. Importantly, and contrary to expectations, the RHD group was similar to normals in continuing to demonstrate an effect of semantic context under conditions of increased processing demands. Results are discussed relative to contemporary theories of laterality, based on studies with normals, that suggest that the involvement of the left versus right hemisphere in context use may depend upon the type of contextual information being processed.

Contextual influences on phonetic identification in aphasia: the effects of speaking rate and semantic bias

Two experiments examined the influence of context on stop-consonant voicing identification in fluent and nonfluent aphasic patients and normal controls. Listeners were required to label the initial stop in a target word varying along a voice onset time (VOT) continuum as either voiced or voiceless ([b]/[p] or [d]/[t]). Target stimuli were presented in sentence contexts in which the rate of speech of the sentence context (Experiment 1) or the semantic bias of the context (Experiment 2) was manipulated. The results revealed that all subject groups were sensitive to the contextual influences, although the extent of the context effects varied somewhat across groups and across experiments. In addition, a number of patients in both the fluent and nonfluent aphasic groups could not consistently identify even endpoint stimuli, confirming phonetic categorization impairments previously shown in such individuals. Results are discussed with respect to the potential reliance by aphasic patients on higher level context to compensate for phonetic perception deficits.

Context use by right-hemisphere-damaged individuals under a compressed speech condition

The effect of increased processing demands on context use by RHD individuals was examined using a word-monitoring task. Subjects were required to monitor for a target word in sentences that were either normal, semantically anomalous, or both syntactically and semantically anomalous. Stimuli were presented at two rates of speech--normal and compressed to 70% of normal. Contrary to expectations, the RHD group performed similar to normals in demonstrating an effect of context at both rates of speech. Results are discussed relative to recent studies of normal brain functioning that suggest that the involvement of the LH versus the RH in context use depends upon the type of contextual information being processed.

Automatic versus strategic effects of phonology and orthography on auditory lexical access in brain-damaged patients as a function of inter-stimulus interval

The influence of both phonological and orthographic information on auditory lexical access was examined in left- and right-hemisphere-damaged individuals using a lexical decision paradigm. Subjects were presented with prime-target pairs that were either phonologically related (tooth-youth), orthographically related (touch-couch), both phonologically and orthographically related (blood-flood), or unrelated (bill-tent), at two inter-stimulus intervals (ISI)--100 ms and 750 ms--to tap more automatic versus more strategic processing. All groups demonstrated effects of orthography at both ISIs (facilitory at 100 ms ISI and inhibitory at 750 ms ISI), supporting the findings by Leonard and Baum (1997) that effects of orthography emerge independent of site of brain damage and suggesting that orthographic effects in auditory word recognition tend to be largely strategic. A facilitory effect of phonology was also found for all groups at both ISIs. The findings are discussed in relation to theories of lexical activation in brain-damaged individuals.

The influence of neighborhood density on phonetic categorization in aphasia

The present study examined the contribution of lexically based sources of information to acoustic-phonetic processing in fluent and nonfluent aphasic subjects and age-matched normals. To this end, two phonetic identification experiments were conducted which required subjects to label syllable-initial bilabial stop consonants varying along a VOT continuum as either /b/ or /p/. Factors that were controlled included the lexical status (word/nonword) and neighborhood density values corresponding to the two possible syllable interpretations in each set of stimuli. Findings indicated that all subject groups were influenced by both lexical status and neighborhood density in making phonetic categorizations. Results are discussed with respect to theories of acoustic-phonetic perception and lexical access in normal and aphasic populations.

Speech timing subsequent to brain damage: effects of utterance length and complexity

Acoustic analyses of syllable durations were conducted in order to address several hypotheses concerning deficits in the control of speech timing subsequent to focal brain damage. Groups of nonfluent and fluent aphasics, right-hemisphere-damaged patients, and normal controls produced monosyllabic root syllables in medial and final position in the context of short and long sentences and syntactically simple and complex sentences. Durations of the target syllable as a proportion of the utterance were compared across contexts and groups. Somewhat surprisingly, the results revealed relatively normal temporal patterns in all subject groups, with the main exception emerging for the nonfluent aphasic patients who failed to demonstrate normal phrase-final lengthening effects. Implications of the findings for theories of temporal control in brain-damaged patients are considered.

Anticipatory coarticulation in aphasia: effects of utterance complexity

The magnitude and extent of anticipatory coarticulation were examined in groups of fluent and nonfluent aphasic patients and normal control subjects. One- and two-syllable target utterances were elicited at slow and fast rates of speech with or without a consonant intervening between the target consonant and vowel, and with or without a preceding schwa, to manipulate utterance complexity. Acoustic analyses (F2 and centroid frequencies) revealed that both groups of aphasic patients exhibited relatively normal patterns of anticipatory coarticulation. However, small but significant differences among the groups emerged in certain conditions. Surprisingly, increased utterance complexity was not found to reduce coarticulatory effects to a greater degree in the nonfluent relative to the fluent aphasic group. Perceptual tests largely confirmed the acoustic analyses.

On-line evidence for context use by right-brain-damaged patients

The ability of right-brain-damaged (RBD) patients to use on-line contextual information in a word-monitoring task was examined. Subjects were required to monitor for target words in the contexts of both normal and semantically anomalous sentences. Similar to previous studies with normals (e.g., Marslen;Wilson & Tyler, 1980), the semantic integrity of the context was influential in the word-recognition process. Importantly, the RDB patients performed similarly to normals in showing context effects. These results were interpreted as substantiating the findings of Leonard, Waters, and Caplan (1997a, 1997b) that RBD patients do not present with a specific deficit in the use of contextual information. The results are discussed in terms of proposals that suggest that an impaired ability to use contextual information by RBD patients may be a function of increased processing demands.

The role of fundamental frequency and duration in the perception of linguistic stress by individuals with brain damage

Two tests of the ability of individuals with left-hemisphere damage (LHD) and right-hemisphere damage (RHD) and non-brain-damaged participants to identify phonemic and emphatic stress contrasts were undertaken. From a set of naturally produced base stimuli, two additional stimulus sets were derived. In one, fundamental frequency (F0) cues to stress were neutralized, whereas in the other duration cues were effectively neutralized. Results demonstrated that individuals with LHD were unable to identify phonemic stress contrasts with better-than-chance accuracy; individuals with RHD performed worse than normal participants but significantly better than the patients with LHD--particularly with the original full-cue stimuli. All groups performed better on the emphatic stress subtest, with the scores of only the patients with LHD at chance level for the F0-neutralized stimuli. The findings are considered in relation to hypotheses concerning the hemispheric lateralization of prosodic processing, particularly with respect to a hypothesis that posits differential lateralization for specific acoustic parameters.

Phonological, semantic, and mediated priming in aphasia

An auditory lexical decision task was conducted to examine rhyme, semantic, and mediated priming in nonfluent and fluent aphasic patients and normal controls. Overall, monosyllabic word targets were responded to faster when preceded by rhyming word and nonword primes than unrelated primes. Similarly, semantically related primes facilitated lexical decisions to word targets. No evidence of mediated priming emerged. Results for individual subjects suggest differences in patterns across the subject groups. Implications of the findings for the integrity of lexical access in aphasic patients are considered.

The development of speech adaptation to an artificial palate

An investigation of adaptation to palatal modification in [s] production was conducted using acoustic and perceptual analyses. The experiment assessed whether adaptation would occur subsequent to a brief period of intensive, target-specific practice. Productions of [sa] were elicited at five time intervals, 15 min apart, with an artificial palate in place. Between measurement intervals, subjects read [s]-laden passages to promote adaptation. Results revealed improvement in both acoustic and perceptual measures at the final time interval relative to the initial measurement period. Interestingly, the data also suggested changes to normal (unperturbed) articulation patterns during the same interval. Results are discussed in relation to the development of speech adaptation to a structural modification of the oral cavity.

The ability of right- and left-hemisphere-damaged individuals to produce and interpret prosodic cues marking phrasal boundaries

Two experiments were conducted with the purpose of investigating the ability of right- and left-hemisphere-damaged individuals to produce and perceive the acoustic correlates to phrase boundaries. In the production experiment, the utterance pink and black and green was elicited in three different conditions corresponding to different arrangements of colored squares. Acoustic analyses revealed that both left- and right-hemisphere-damaged patients exhibited fewer of the expected acoustic patterns in their productions than did normal control subjects. The reduction in acoustic cues to phrase boundaries in the utterances of both patient groups was perceptually salient to three trained listeners. The perception experiment demonstrated a significant impairment in the ability of both left-hemisphere-damaged and right-hemisphere-damaged individuals to perceive phrasal groupings. Results are discussed in relation to current hypotheses concerning the cerebral lateralization of speech prosody.

Unilateral brain damage, prosodic comprehension deficits, and the acoustic cues to prosody

Stimuli from two previously presented comprehension tasks of affective and linguistic prosody (Pell & Baum, 1997) were analyzed acoustically and subjected to several discriminant function analyses, following Van Lancker and Sidtis (1992). An analysis of the errors made on these tasks by left-hemisphere-damaged (LHD) and right-hemisphere-damaged (RHD) subjects examined whether each clinical group relied on specific (and potentially different) acoustic features in comprehending prosodic stimuli (Van Lancker & Sidtis, 1992). Analyses also indicated whether the brain-damaged patients tested in Pell and Baum (1997) exhibited perceptual impairments in the processing of intonation. Acoustic analyses of the utterances reaffirmed the importance of F0 cues in signaling affective and linguistic prosody. Analyses of subjects' affective misclassifications did not suggest that LHD and RHD patients were biased by different sets of the acoustic features to prosody in judging their meaning, in contrast to Van Lancker and Sidtis (1992). However, qualitative differences were noted in the ability of LHD and RHD patients to identify linguistic prosody, indicating that LHD subjects may be specifically impaired in decoding linguistically defined categorical features of prosodic patterns.

The ability to perceive and comprehend intonation in linguistic and affective contexts by brain-damaged adults

Receptive tasks of linguistic and affective prosody were administered to 9 right-hemisphere-damaged (RHD), 10 left-hemisphere-damaged (LHD), and 10 age-matched control (NC) subjects. Two tasks measured subjects' ability to discriminate utterances based solely on prosodic cues, and six tasks required subjects to identify linguistic or affective intonational meanings. Identification tasks manipulated the degree to which the auditory stimuli were structured linguistically, presenting speech-filtered, nonsensical, and semantically well-formed utterances in different tasks. Neither patient group was impaired relative to normals in discriminating prosodic patterns or recognizing affective tone conveyed suprasegmentally, suggesting that neither the LHD nor the RHD patients displayed a receptive disturbance for emotional prosody. The LHD group, however, was differentially impaired on linguistic rather than emotional tasks and performed significantly worse than the NC group on linguistic tasks even when semantic information biased the target response.

Compensation for jaw fixation by aphasic patients

The ability to compensate for fixation of the jaw by a bite block was investigated in 6 nonfluent aphasics, 6 fluent aphasics, and 10 normal control subjects. Acoustic analyses of the vowels [i u a ae] and fricatives [s s] revealed substantial but incomplete compensation for the perturbation in all three subject groups. Perceptual identification scores and quality ratings by naive and phonetically trained listeners indicated poorer identification of the high vowels [i u] under compensatory conditions relative to normal production. Of particular interest was the fact that all three groups of subjects exhibited similar patterns of results. The findings suggest that any deficit in speech motor programming demonstrated by the nonfluent aphasic patients did not affect compensatory abilities. Results are discussed with respect to normal speech adaptation skills and the nature of articulatory breakdown in nonfluent aphasia.

Speech compensation to structural modifications of the oral cavity

Acoustic and perceptual analyses of vowels, stops, and fricatives produced with and without an artificial palate were conducted. Recordings were made both immediately upon insertion of the palate and following a 15-min adaptation period. Results of the acoustic analyses revealed significant alterations in the fricative spectra under conditions of perturbation with fewer, if any, changes in the vowels and stop consonants. Perceptual data confirmed these patterns and provided evidence of possible improvements in compensation over time. The data are compared to our previous studies of speech sound articulation under bite-block conditions. Differences between adaptation to modifications of oral structure (artificial palate) and oral function (jaw fixation by a bite block) are considered.

Compensation to articulatory perturbation: perceptual data

The perceptual adequacy of vowels, stop consonants, and fricatives produced under conditions of articulatory perturbation was explored. In a previous study [McFarland and Baum, J. Acoust. Soc. Am. 97, 1865-1873 (1995)], acoustic analyses of segments produced in two subtests (immediate compensation and postconversation) revealed small but significant changes in spectral characteristics of vowels and consonants under bite-block as compared to normal conditions. For the vowels only, adaptation increased subsequent to a period of conversation with the bite block in place, suggesting that compensation may develop over time and that consonants may require a longer period of adaptation. The present follow-up investigation examined whether the acoustic differences across conditions were perceptually salient. Ten listeners performed an identification and a quality rating task for stimuli from the earlier acoustic study. Results revealed reductions in identification scores and quality ratings for a subset of the vowels and consonants in the bite-block conditions relative to the normal condition in the immediate compensation subtest. In the postconversation subtest, quality ratings for the fricatives in the bite-block condition remained low as compared to those in the normal condition. Perceptual results are compared to the previous acoustic data gathered on these stimuli.

Fricative production in aphasia: effects of speaking rate

The present study investigated the effects of alterations in speaking rate on the production of the fricatives [f s v z] by 10 nonfluent aphasics, 7 fluent aphasics, and 10 normal control subjects. An examination of fricative consonants allowed us to address whether previous conflicting findings for vowels and stop consonants produced by nonfluent aphasic patients were due to basic differences in the treatment of major sound classes or to differences in the length of the segments under investigation. Acoustic analyses revealed that all subjects were able to manipulate rate of speech. Both groups of aphasic patients produced rate changes that were smaller in magnitude than those of the normal subjects. Further analyses demonstrated that both the fluent and the nonfluent aphasic patients were able to instantiate the rate changes in terms of fricative duration. However, both patient groups exhibited breakdowns in the ability to maintain contrastive differences between voiced and voiceless fricatives, particularly at fast rates of speech. Possible sources of these breakdowns are explored.

Incomplete compensation to articulatory perturbation

Measurements were made of vowels, fricatives, and stop consonants produced by 15 adult speakers of French in one free-mandible and two fixed mandible conditions. Speech acoustic data were recorded immediately upon bite-block insertion and after a 15-min accommodation period. Results indicate that compensation to increased jaw opening during speech is neither immediate nor complete as there were small but significant differences in the acoustic parameters of vowels and consonants produced under bite-block and normal conditions. Further, the data suggest that, at least for vowels, speech compensatory strategies may develop over time, perhaps involving error-based correction. Consonants appear to require a more lengthy period of speech adaptation, and this may be due to the articulatory requirements for their accurate production. Individual differences in compensatory abilities are also discussed.

Rhyme priming in aphasia: the role of phonology in lexical access

The present experiment was conducted to explore the facilitory effects of rhyme in lexical processing in brain-damaged individuals. Normal subjects and non-fluent and fluent aphasic subjects performed auditory lexical decision and rhyme judgement tasks, in which prime-target pairs were phonologically related (either identical or rhyming) or unrelated. Results revealed rhyme facilitation of lexical decisions to real-word targets for normal and non-fluent aphasic subjects; for fluent aphasic subjects, results were equivocal. In the rhyme judgement task, facilitory effects of rhyme were found for all three groups with real-word targets. None of the groups showed clear rhyme facilitation effects with non-word targets in either task. Findings are discussed with reference to the role of phonology in lexical processing in normal and aphasic populations.

Perception of coarticulatory cues in the speech of children with profound hearing loss and children with normal hearing

Two experiments investigated the perception of coarticulatory cues in the speech of children with profound hearing loss and children with normal hearing. To examine anticipatory coarticulation, five repetitions of the syllables [section i section u ti tu ki ku] produced by nine children with hearing loss and nine children with normal hearing were edited to include only the aperiodic consonantal portion. To explore perseveratory coarticulation, comparable segments were excised from the syllables [i section u section it ut it uk]. The stimuli had been analyzed previously in two acoustic studies of coarticulation (Baum & Waldstein, 1991; Waldstein & Baum, 1991). Ten listeners were presented with the aperiodic segment and were asked to identify the missing vowel. Overall, listeners' vowel identification was better for the productions by children with normal hearing than for those by children with hearing loss. In anticipatory contexts, listeners were able to identify the absent vowel with better-than-chance accuracy for all productions by both groups except the [i] tokens following [section] produced by children with hearing loss. In perseveratory contexts, identification accuracy was significantly above chance for all except the [i] tokens preceding [t] produced by children with normal hearing, but only for [u] tokens produced by children with hearing loss. Identification accuracy was better in anticipatory than in perseveratory contexts for both speaker groups' productions. The patterning of vowel identification, however, differed for the two speaker groups in anticipatory but not perseveratory contexts.

Rate of speech effects in aphasia: voice onset time

This study investigated the ability to produce appropriate voice onset time (VOT) contrasts under conditions of rate modulation in groups of nonfluent aphasic subjects, fluent aphasic subjects, and nonneurological controls. Acoustic analyses of the consonants [b d g p t k] produced in the context of the vowels [i e a o u] at two different rates of speech revealed that normal subjects' VOTs were significantly shorter at the fast rate of speech relative to the slow/normal rate, as expected. In addition, the rate change had a significantly greater effect on voiceless stops as compared to voiced and on velar consonants as compared to labials and alveolars. The nonfluent aphasic patients exhibited a similar pattern except that no differences in magnitude of rate-related changes were found across place of articulation. Further, similar to previous studies, the nonfluent aphasic patients produced voice and voiceless consonants with somewhat overlapping VOT distributions, indicating an impairment in temporal integration in these subjects. Finally, the fluent aphasic patients demonstrated a surprisingly aberrant pattern of results, with VOTs under th fast condition shorter than under the slow, but no differences in magnitude of change across place of articulation or voicing categories. The results are discussed in relation to the nature of speech production deficits in both nonfluent and fluent aphasic patients. Implications for remediation are considered.

An acoustic analysis of rate of speech effects on vowel production in aphasia

The present investigation examined the production of tense and lax vowel duration differences at two speaking rates in the speech of 10 nonfluent aphasics, 8 fluent aphasics, and 10 normal control subjects. Subjects produced four repetitions of each of the vowels [i e ae o u I epsilon upsilon --] at each speaking rate. Acoustic analyses revealed that subjects in all three groups were able to manipulate overall rate of speech. In addition, normal controls and fluent aphasic subjects produced vowels under the fast rate condition which were significantly shorter than those under the slow rate condition. Despite a change in overall speaking rate, the nonfluent aphasics did not exhibit a significant difference in vowel duration at the two rates of speech, suggesting a deficit in the implementation of this temporal parameter. Both normal controls and fluent aphasic patients produced nonoverlapping distributions of tense and lax vowels at both speaking rates. In contrast, the nonfluent aphasics demonstrated a great deal of overlap in the distribution of tense and lax vowel durations at the fast rate. Results are discussed in relation to the nature of the speech production deficits in nonfluent and fluent aphasic patients.

Lexical effects on the phonetic categorization of speech: the role of acoustic structure

This study examines the extent to which acoustic parameters contribute to lexical effects on the phonetic categorization of speech. Experiment 1 was designed to replicate previous findings. Two test continua were created varying in voice onset time. Results of both identification and reaction time (RT) range data showed an effect of lexical status at the phonetic boundary, but only in the slowest RT ranges, suggesting that lexical effects on phonetic categorization are postperceptual. Experiment 2 explored whether the lexical effect would emerge when the stimulus continua more nearly approximated the parameter values of natural speech. Both identification and RT range data indicated that the lexical effect disappeared. These results suggest that without attention to the acoustic structure of the stimuli, the role of top-down processing in phonetic categorization may be overemphasized.

Lexical effects on the phonetic categorization of speech: The role of acoustic structure

This study examines the extent to which acoustic parameters contribute to lexical effects on the phonetic categorization of speech. Experiment 1 was designed to replicate previous findings. Two test continua were created varying in voice onset time. Results of both identification and reaction time (RT) range data showed an effect of lexical status at the phonetic boundary, but only in the slowest RT ranges, suggesting that lexical effects on phonetic categorization are postperceptual. Experiment 2 explored whether the lexical effect would emerge when the stimulus continua more nearly approximated the parameter values of natural speech. Both identification and RT range data indicated that the lexical effect disappeared. These results suggest that without attention to the acoustic structure of the stimuli, the role of top-down processing in phonetic categorization may be overemphasized.

Acoustic analyses and perceptual data on anticipatory labial coarticulation in adults and children

The present study investigated anticipatory labial coarticulation in the speech of adults and children. CV syllables, composed of [s], [t], and [d] before [i] and [u], were produced by four adult speakers and eight child speakers aged 3-7 years. Each stimulus was computer edited to include only the aperiodic portion of fricative-vowel and stop-vowel syllables. LPC spectra were then computed for each excised segment. Analyses of the effect of the following vowel on the spectral peak associated with the second formant frequency and on the characteristic spectral prominence for each consonant were performed. Perceptual data were obtained by presenting the aperiodic consonantal segments to subjects who were instructed to identify the following vowel as [i] or [u]. Both the acoustic and the perceptual data show strong coarticulatory effects for the adults and comparable, although less consistent, coarticulation in the speech stimuli of the children. The results are discussed in terms of the articulatory and perceptual aspects of coarticulation in language learning.